Foams (foamed molded articles) have been used as internal insulators of electronic devices and information devices, cushioning materials, dust proofing materials, sound insulating materials, heat insulating materials, food packing materials, clothing materials, building materials, interior parts or exterior parts of automobiles and home electric appliances, and the like. Such foams are required to have characteristics such as flexibility, cushioning properties and heat insulating properties, from the viewpoint of securing sealing properties thereof when incorporated as parts. As materials for the foams, resin foams based on polyolefins such as polyethylene and polypropylene have been known. However, these foams have a problem of being insufficient in terms of flexibility and cushioning properties. As an attempt for solving such a problem, it has been conducted to soften the material itself by raising expansion ratio or by incorporating a rubber ingredient or the like into a polyolefin resin. However, ordinary polyethylene or polypropylene is weak in tension at high temperature, namely, in melt tension, and even when it is attempted to obtain high expansion ratio, cell walls collapse at the time of foaming, thereby causing gas escape and cell linking. It has therefore been difficult to obtain a soft foam having the desired high expansion ratio.
In order to solve the above-mentioned problems, JP-A-2004-250529 discloses a polyolefin resin foam produced by foam-molding a composition for the polyolefin resin foam having a melt tension of 20 cN or more, which contains a polymer component composed of a polyolefin resin and a rubber and/or a thermoplastic olefin elastomer, and powdery particles. However, there has been still room for improvement in terms of flexibility, cushioning properties, cutting processability and the like of the obtained foam.
Further, accompanied with recent progress of miniaturization of electronic devices and information devices, foams used as internal insulators or cushioning materials have also come to be required to be small in width and thickness. However, in the foam containing the conventional polyolefin resin material, strain on compression is large, especially when the processing width is narrow. For example, at the time of punching processing, cells in a punching site collapse to become difficult to recover the shape of the foam, thereby causing a problem that an upper end portion of the punching site becomes roundish or that the thickness of the punching site (end portion) becomes thin.